public class test01 {
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode() {}
     *     TreeNode(int val) { this.val = val; }
     *     TreeNode(int val, TreeNode left, TreeNode right) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
        public TreeNode invertTree(TreeNode root) {
            if(root==null){
                return root;
            }
            TreeNode tmp = root.right;
            root.right = root.left;
            root.left = tmp;
            invertTree(root.left);
            invertTree(root.right);

            return root;
        }
}
